Isothermal reactor for exothermic or endothermic heterogeneous reactions

ABSTRACT

An isothermal reactor for carrying out heterogeneous exothermic or endothermic reactions, includes within a catalytic bed ( 3 ) housed in an appropriate outer shell ( 2 ), at least one tube ( 13 ) for the passage of a cooling or heating fluid which advantageously extends within the bed ( 3 ) along a plane substantially perpendicular with respect to opposed perforated side walls ( 4, 5 ) of the catalytic bed.

This is a National Stage entry of Application PCT/EP00/05470, with aninternational filing date of Jun. 14, 2000, which was published as WOPublication No. 00/76652 A1, and the complete disclosure of which isincorporated into this application by reference.

FIELD OF APPLICATION

The present invention relates to an isothermal reactor for carrying outexothermic or endothermic heterogeneous reactions, comprising:

-   -   a preferably vertical, outer shell of substantially cylindrical        shape;    -   at least one catalytic bed provided in the shell and comprising        opposed perforated side walls for the inlet of a flow comprising        reactants and the outlet of a flow comprising reacted        substances, respectively; and    -   at least one tube passing through said at least one catalytic        bed for the passage of a cooling or heating fluid.

In the following description and attached claims, with the term:“isothermal reactor”, it is intended to mean a reactor wherein thetemperature within the catalytic bed(s) where the reaction takes placeis maintained essentially constant, such reaction may be eitherexothermic or endothermic.

Reactors of this kind may for example be employed in the synthesis ofchemicals such as methanol or formaldehyde (strongly exothermicreactions) or styrene (strongly endothermic reactions).

As known, in the field of exothermic or endothermic heterogeneoussynthesis, the need is more and more felt of realizing isothermalreactors of high capacity that on one side are easy to manufacture,reliable and require low investment and maintenance costs, and on theother side allow to operate with low pressure drops, low energyconsumption and with a high heat exchange efficiency between thereactants and the cooling or heating fluid.

PRIOR ART

In order to comply with the above mentioned need, isothermal reactorshave been proposed in the field, which are provided with a catalytic bedof radial type comprising a large number of vertical straight tubeswithin it for drawing off or supplying heat.

For example, DE-A-3 318 098 discloses an isothermal reactor for carryingout exothermic or endothermic heterogeneous syntheses wherein thegaseous reactants pass through the catalytic bed radially and come incontact with a plurality of vertical tubes arranged within said bed.

According to an embodiment which is not shown, it is also foreseen thatthe tubes for drawing off or supplying the heat extends helically abouta central collector for the outlet of the reacted gases from thereactor.

In particular, the bundle of helicoidal tubes extends vertically betweenopposed upper and lower tube plates, wherein such tubes are twistedround each other.

It shall be noticed that helicoidal arrangements for the tubes fordrawing off or supplying heat are known also in the isothermal reactorsprovided with axial catalytic bed. See for instance U.S. Pat. No.4,339,413 and U.S. Pat. No. 4,636,365.

Although advantageous under certain aspects (for example, the radialarrangement of the catalytic bed allows to obtain in an easy andcost-effective way higher production capacities with lower pressuredrops and lower energy consumption than with an axial bed), theisothermal reactor with a helicoidal tube bundle disclosed in DE-A-3 318098 has a number of drawbacks, which are set forth hereinbelow.

First of all, the arrangement of the tubes as a helicoidal tubebundle—although better than the arrangement of vertical straighttubes—does not match effectively the temperature curve of the flow ofgaseous reactants that pass through the catalytic bed with a radialmotion.

In fact, the gas flow flowing perpendicularly with respect to thevertical extension of the helicoidal tubes, comes in contact—passingthrough the catalytic bed—with different tubes at differenttemperatures, and this causes a low heat exchange efficiency between thegaseous reactants and the cooling or heating fluid.

In other words, in case of exothermic reactions with the gaseousreactants that flow in centripetal radial motion through the catalyticbed, the outer helicoidal tubes are crossed by a gas that has juststarted to react, and is thus relatively cold, whereas the helicoidaltubes which are closer to the core are crossed by a gas at higher andhigher temperature that exchanges with them an ever increasing amount ofheat until a point is reached, where the temperature of the reaction gasis at its maximum. From there on, the temperature decreases and hencethe amount of heat which is absorbed by the helicoidal tubes arrangednext to the gas outlet wall of the catalytic bed is progressivelysmaller. (see DE-A-3 318 098, FIG. 3).

Therefore, each helicoidal tube receives a different amount of heat andmust stand a different thermal load. This causes a bad distribution oftemperature within the catalytic bed detrimental for the heat exchangeefficiency.

For example, whenever hot water flows inside the tubes as cooling means,and it is transformed into steam, it is clear that each tube of ahelicoidal tube bundle as suggested in DE-A-3 318 098, produces adifferent amount of steam.

This implies relevant problems of control and feed/draw off for thecooling fluid at the tube plates, as well as a bad distribution of thewater and of the steam inside said tubes.

In this respect, it is worth noticing how all the tubes of theisothermal reactor described in DE-A-3 318 098 are parallel to eachother, that is to say they are fed from the same source and discharge atthe same point. Hence the pressure drop available for each helicoidaltube is the same.

In DE-A-3 318 098, the helicoidal tubes in contact with the gaseousreactants at low temperature are subjected to a small thermal load,which means a low degree of vaporization of the water with ensuing lowoutlet velocity and therefore high water flow rates (calculated as massflow rates). The helicoidal tubes in contact with the gaseous reactantsat high temperature are instead subjected to a great thermal load, whichmeans a high degree of vaporization of the water with ensuing highoutlet velocity and therefore low water flow rates (calculated as massflow rates).

Therefore, when the reactor is operating, a situation occurs wherein thecoils which undergo the greatest thermal load are those which aresupplied with less water and are prone to have an ever increasing degreeof vaporization and an ever decreasing capacity of drawing off the heat.This brings to a far from optimum distribution of temperature within thecatalytic bed, in case of slightly exothermic reactions such as themethanol synthesis whilst in case of fast and strongly exothermicreactions such as the formaldehyde synthesis, this may even bring to atemperature sharp rise.

Further on, the excessive vaporization promotes the formation inside thetubes of deposits of residues present in the water to the detriment ofthe heat exchange efficiency of the tubes themselves.

All these disadvantages are independent from the fact that the tubes arearranged at different distances depending on the profile of temperatureof the gaseous reactants within the catalytic bed.

A further disadvantage of the reactor according to the prior art isgiven by the high structural complexity deriving from the helicoidalarrangement of the tube bundle that requires high investment andmaintenance costs.

Further on, the provision of tube plates—which generally need to be verythick and hence expensive because of the difference of pressure betweenthe gaseous reactants and the cooling or heating fluid—is a constraintas far as the number of tubes which may be arranged is concerned, withensuing further detriment of the heat exchange efficiency of thereactor.

Because of these disadvantages, isothermal reactors for carrying outexothermic or endothermic heterogeneous syntheses with a radialcatalytic bed and a helicoidal tube bundle have been indeed used quiteseldom to date (and this is even more true for reactors with a verticaltube bundle), notwithstanding the ever increasing need felt in the fieldof having high capacity reactors.

SUMMARY OF THE INVENTION

The problem underlying the present invention is that of providing anisothermal reactor for carrying out exothermic or endothermicheterogeneous reactions which is easy to realize, reliable and requireslow investment and maintenance costs and allows to operate with lowpressure drop, low energy consumption and with a high heat exchangeefficiency between the reactants and the cooling or heating fluid.

The aforesaid problem is solved, according to the invention, by areactor of the above mentioned type, that is characterized in that saidat least one tube for drawing off or supplying heat extends within saidat least one catalytic bed along a plane substantially perpendicularwith respect to the side walls of the bed.

Thanks to the present invention, it is advantageously possible torealize—in an easy and cost-effective way—an isothermal reactor with ahigh heat exchange coefficient, to all advantage of the conversion yieldand of the energy consumption.

In fact, differently from the helicoidal tubes according to the priorart that extend from one end to the other of the catalytic bed in adirection substantially parallel with respect to the perforate sidewalls for the feed and extraction of the gaseous flow, according to thepresent invention each single tube for drawing off or for supplying heatextends along a plane within the catalytic bed substantiallyperpendicular with respect to the side walls for the passage of thereactants.

In this way, the tube(s) is (are) advantageously arranged in asubstantially parallel way with respect to the direction of crossing ofthe catalytic bed by the flow comprising reactants.

This means that each single tube is in contact with a same portion ofreactants and matches advantageously all the heat variations, and hencethe temperature profile, of such portion of reactants from the inlet tothe outlet of the catalytic bed.

By consequence, whenever within the catalytic bed(s), a plurality oftubes is arranged according to the present invention, they all withstandthe same thermal load. For example, in case of an exothermic reaction,with hot water as cooling fluid, all the tubes produce the same amountof steam (uniform distribution of the water and steam inside the tubes).

In other words, thanks to the present invention, each tube is able todraw off or to supply the same amount of heat and it is thus possible toobtain an optimum distribution of the temperature within the catalyticbed, also for strongly exothermic or endothermic reactions. This is toall advantage of the heat exchange efficiency of the catalytic bed andhence of the conversion yield inside the bed itself and of therespective energy consumption.

With respect to the above described isothermal reactor with reference tothe prior art, the reactor according to the present invention allows torecover or supply heat at a higher thermal level, with ensuing increaseof the heat exchange efficiency and of the conversion yield. Or, again,the conversion yield being the same as for the prior art, the increaseof the heat exchange efficiency permits to decrease the requiredcatalyst volume, with ensuing savings in terms of space and investmentcosts.

A further advantage of the present invention is that, when a pluralityof tubes are arranged inside a catalytic bed, these may all be fed froma same source as there are no control problems for the supply andextraction of the cooling/heating fluid, all the tubes being subjectedto the same thermal load.

Finally, it shall be noticed how the reactor according to the presentinvention is particularly easy to be realized and does not require tubeplates, with ensuing relevant savings in terms of investment andmaintenance costs.

The features and the advantages of the present invention will becomeclear from the following indicative and non-limiting description of anembodiment of the invention, made with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In such drawings:

FIG. 1 shows a partial view in longitudinal section of an isothermalreactor for carrying out exothermic or endothermic heterogeneousreactions according to an embodiment of the present invention;

FIG. 2 shows an enlarged schematic prospective view of a detail of thereactor of FIG. 1;

FIG. 3 shows an enlarged schematic view in longitudinal section of adetail of the reactor of FIG. 1;

FIG. 4 shows a schematic view in cross section of a coil tube atconstant pitch for the passage of a cooling or heating fluid, of thetype employed in the reactor of FIG. 1;

FIG. 5 shows a schematic view in cross section of the tube of FIG. 4 atvariable pitch;

FIG. 6 shows a view in longitudinal section of an isothermal reactor forcarrying out exothermic or endothermic heterogeneous reactions accordingto a further embodiment of the present invention;

FIG. 7 shows a schematic view in cross section of two coil tubesarranged side-by-side for the passage of a cooling or heating fluid, ofthe type employed in the reactor of FIG. 6;

FIG. 8 shows a schematic view in cross section of two tubes arrangedside-by-side for the passage of a cooling or heating fluid, according toa further embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to FIGS. 1–5, an isothermal reactor according to thepresent invention for carrying out exothermic or endothermicheterogeneous reactions is indicated in its whole with 1.

The reactor 1 comprises an outer shell 2 of substantially cylindricalshape, inside which a catalytic bed is housed, generally indicated with3.

The catalytic bed 3 is delimited on its sides by opposed perforated sidewalls 4 and 5, for the inlet of a flow comprising reactants and for theoutlet of a flow comprising reacted substances, respectively.

Generally speaking, the substances which are fed to the reactor 1 forcarrying out the exothermic or endothermic heterogeneous syntheses arein gaseous phase.

Therefore, in the description below, with the terms: “flow comprisingreactants” and “flow comprising reacted substances”, it is intended tomean a flow of gaseous reactants and a flow of reacted gases,respectively. It is anyway clear that the reactor according to thepresent invention might be employed also for reactions occurring inliquid phase or liquid/gaseous phase, respectively.

In the example described hereinbelow, the perforated walls 4 and 5 arehence gas permeable with respect to the inlet in the catalytic bed 3 ofa flow of gaseous reactants and to the outlet of a flow of reactedgases, respectively.

The catalytic bed 3 is further delimited in its lower part by anunperforated bottom (not permeable to gases), that corresponds in theexample of FIG. 1 with the bottom 6 of the reactor 1, and in its upperpart by a perforated wall 7 (gas permeable) for the passage with axialmotion through the bed 3 of a minor portion of the gaseous reactants.

In order to allow a correct axial-radial crossing of the catalytic bed3, the radial part being preponderant with respect to the axial part,the side wall 5 has a small unperforated portion 5′ (not permeable togases) that extends from an upper end thereof.

The wall 7 permeable to gases is anyway totally optional, featuringmainly the function of holding the catalyst (not represented in FIG. 1)inside the bed 3, so that it may be well left apart.

Alternatively, whenever a merely radial crossing of the catalytic bed isrequired, a wall 7 is provided, which is not perforated or anyway notpermeable to the gas.

Both the catalytic bed of the radial type and, even in a more remarkableway, that of the axial-radial type are particularly advantageous as theyallow to obtain high conversion yields and at the same time low pressuredrops for the gaseous reactants, by making use of more active catalystsof smaller granulometry.

Between the shell 2 and the side wall 4 there is provided an annularspace 8 for allowing an optimum distribution and feed of the gaseousreactants in the catalytic bed 3. To this end, the space 8 is in fluidcommunication with a gas inlet nozzle 9.

In turn, the side wall 5 defines inside it a duct 10 for the collectionand ejection from the reactor of the flow of reacted gases. To this end,the duct 10 is in fluid communication with a gas outlet nozzle 11 and isclosed on its upper side by a baffle 12 not permeable to gases.

In order to allow the draw off or the supply of heat from or to thegases flowing inside the catalytic bed 3, so as to maintain the reactor1 isothermal, the bed 3 is crossed by a plurality of tubes, which areall indicated by numeral 13, for the passage of a cooling or heatingfluid, respectively.

The cooling or heating fluid is fed to the tube 13 through a duct 14 influid communication with one or more inlet nozzles 15, and extractedfrom the tubes 13 through a duct 16 in fluid communication with one ormore outlet nozzles 17.

The number of nozzles 15 and 17, respectively, (equal to two as far asthe instant example is concerned) is chosen according to the cooling orheating fluid flow rate. Preferably, the more relevant such flow rate,the larger the number of outlet nozzles 15 and 17.

The duct(s) 14 are in fluid communication with the nozzle(s) (15)through a toroidal collector 14 a, whereas the duct(s) 16 are in fluidcommunication with the nozzle(s) 17 through a toroidal collector 16 a.

According to a particularly advantageous aspect of the presentinvention, the tubes 13 for drawing off or supplying heat, extend as acoil within the catalytic bed 3 along a plane substantiallyperpendicular with respect to the side walls 4 and 5 thereof.

In the following description and attached claims, with the term: “coiltube ”, it is intended to mean a tube which is substantially curvilinearor provided alternatively with curvilinear and straight sections.

In doing so, each tube 13 is crossed for all its length by a sameportion of reactant gases, thus being able to follow all the thermalvariations, and hence the temperature profile, of such gas portion fromthe inlet to the outlet of the catalytic bed 3.

In addition, the tubes 13 formed as a coil along respective planessubstantially parallel to each other, all undergo the same thermal loadand operate hence in the same way.

This results in an optimal distribution of the temperatures inside bed3, without the risk of sharp temperature rises, and an efficient heatexchange between the gaseous reactants and the cooling or heating fluidto all advantage of the conversion yield and of the energy consumption.

In the example of FIG. 1, the shell 2 is arranged vertically and thetubes 13 extend as coils within the catalytic bed 3 along a plane thatis preferably substantially horizontal.

Nothing prevents, anyway, from arranging the tubes 13 in a differentway, for example in groups of tubes overlaid with respect to each other,which extend along vertical planes.

In both instances, the tubes are perpendicular with respect to the sidewalls 4 and 5, as well as with respect to the longitudinal axis 18 ofthe shell 2 in case of a vertical reactor, whereas they aresubstantially parallel with respect to the crossing direction of the bed3 by the flow of gaseous reactants.

It is clear, that within the scope of the present invention, there isalso foreseen a reactor 1 comprising a plurality of catalytic beds 3,wherein the beds may be crossed by a variable number of tubes 13 (atleast one) according to the exothermal degree of the reaction and/or thedimensions of the catalytic bed.

In the scope of the present invention it is also comprised a reactor 1comprising one or more catalytic beds crossed by the flow of reactantswith mainly radial motion from the centre (duct 10) towards the outerperiphery (space 8).

Still, according to a further, not shown, embodiment of the presentinvention, it is possible to foresee an outer shell of the horizontaltype comprising one or more catalytic beds crossed by tubes for drawingoff or supplying heat, that extend as coils along planes perpendicularwith respect to the gas-permeable walls for the inlet and outlet of thegaseous reactants. In this case, as well, the perforated side walls ofthe catalytic bed(s) are parallel with respect to the longitudinal axisof the shell.

The tubes 13 may be singularly connected to the nozzles 15 and 17, andhence each tube 13 is connected to a feed duct 14 and a duct 16 fordrawing off the cooling or heating fluid, respectively. They may also beconnected to groups of at least two tubes, i.e. to a duct 14 and a duct16 for each group of tubes 13, or through a single duct 14 or 16,respectively, so that all the tubes 13 are connected to each other.

Preferably, the tubes 13 are connected to each other—at respective freeends—in groups of at least two tubes, each group being in fluidcommunication with a duct 14 for feeding and a duct 16 for drawing offthe cooling or heating fluid, respectively. The various ducts 14 and 16are, in turn, in fluid communication with the nozzle 15 and with thenozzle 17, respectively.

The connection between single adjacent tubes is accomplished by means ofconnecting pipes, all indicated with 19, as better shown in FIGS. 2 and3.

In case of a plurality of ducts 14 and 16, these lead into therespective collectors 14 a and 16 a as well as into the respective tubes13 preferably at an angularly offset position with respect to eachother.

In the example of FIG. 1, the first and the last group of tubes 13comprised in the catalytic bed 3 are shown.

The cooling or heating fluid is fed by means of respective ducts 14 incorrespondence of one end of the lower tubes 13 of each group, is madeto pass through the tubes 13 of each group, wherein heat exchangers ofthe same entity take place, and finally drawn off by means of respectiveducts 16 from an end of the upper tubes 13 of each group.

Alternatively, it is possible to provide for a crossing of the groups oftubes by the cooling or heating fluid in a direction downwards. In thiscase, the fluid is fed to the tubes 13 through the ducts 16 and is drawnthrough the ducts 14.

It shall be noticed how the resulting construction is easy to realizeand to operate, and how the provision of a tube plate is not required,with ensuing savings in terms of investment and maintenance costs withrespect to the prior art.

The embodiment shown in FIG. 1 is more advantageous than the one whereineach single tube 13 is separately connected to the nozzles 15 and 17,particularly for long reactors which are provided with a lot of tubes13. In fact, the number of ducts 14 and 16 is reduced (depending on thenumber of tubes 13 making up each group).

Further on, the embodiment shown in FIG. 1 is more advantageous than theone wherein all the tubes 13 are connected to each other, with the tubesat the respective lower and upper ends connected to a single duct 14 and16, respectively, as there is a lower pressure drop for the cooling orheating fluid.

On the other hand, the structure with all the tubes 13 being connectedto each other, is particularly easy to be realized, as it needs only onefeed duct 14 and one drawing off duct 16 for the cooling or heatingfluid.

Preferably, the tube(s) 13 crossing the catalytic bed 3 for drawing offor for supplying heat are realized with a spiral-shaped coil as shown inFIGS. 4 and 5.

In fact, the spiral shape of tubes 13 has been found to be particularlyadvantageous both in terms of heat exchange efficiency and in terms ofsimplicity and flexibility of construction.

The spiral-shaped tube 13 may adapt itself to the most varyingdimensions of the catalytic bed 3, and in particular it is able to coverall the portions of the same, thus allowing an effective heat exchangeto take place everywhere in the bed.

Further on, according to the amount of heat to be drawn off or to besupplied, the spiral-shaped tube 13 may be realized with turns at a moreor less close distance.

In the example of FIG. 4, the spiral tube is realized with a constantwinding pitch, that is to say a constant distance between two adjacentturns.

In this respect, particularly advantageous results have been obtainedvarying the winding pitch in accordance with the variation of the radiusof the spiral, in such a way to adapt itself to the temperature profileof the gaseous reactants within the catalytic bed 3, following all itsthermal variations.

In this instance, shown in FIG. 5, the distance between adjacent turnsvaries in accordance with the variation of the radius of the spiral and,preferably, the winding pitch decreases as the spiral radius increases.

In order to take into account in the best way the heterogeneousdistribution of the flow of gaseous reactants in the catalytic bed 3, inparticular for an axial-radial bed, the tubes 13 may be advantageouslyarranged at a varying distance between the planes of two adjacent tubes.

In doing so, it is possible to adapt the distance of the tubes 13according to the amount of heat to be drawn off or to be supplied, inother words, following the temperature profile in the catalytic bed 3,to all advantage of the degree of heat exchange efficiency, whichfavorably affects the conversion yield and the energy consumption.

According to this embodiment, not shown, it is possible to obtain ahigher concentration of tubes 13 (smaller distance between the planes oftwo adjacent tubes) where a higher flow rate of gaseous reactants andhence greater thermal loads is to be found, and a lower concentration oftubes 13 (larger distance between the planes of two adjacent tubes)where the flow rate is lower.

In FIG. 6 an isothermal reactor is shown, for carrying out exothermic orendothermic heterogeneous reactions according to a further embodiment ofthe present invention.

In such figure, the details of reactor 1 which are equivalent to thoseillustrated in FIG. 1 from the structure and operation point of view,will be indicated with the same reference numerals and will not bedescribed any more.

In the example of FIG. 6, it is important to notice how incorrespondence of a predetermined horizontal plane two tubes 13 arrangedside-by-side are provided, as better shown in FIG. 7. Heat exchanges ofequal entity take place inside the tubes 13 arranged side-by-side.

All the tubes 13 of each series 20 and 21, respectively, areadvantageously connected to each other by means of connecting pipes 19,so as to form two parallel series of tubes 13, generally indicated with20 and 21. Further on, each series 20, 21 is connected by means ofrespective lower and upper tubes 13 to only one feed duct 14 and drawingoff duct 16 for the cooling or heating fluid, respectively.

In particular, the tubes 13 extend as a coil having the shape of an arcof a circle of increasing length from a central zone to a peripheralzone.

The tubes 13 of each series 20, 21 may be of course arranged divided ingroups inside the reactor of FIG. 6, such as in the example of FIG. 1.

The main difference with respect to the example of FIG. 1 is given bythe fact that in such example each single tube 13 extended along theentire section of the catalytic bed 3, while now the tubes 13, which arearranged side-by-side, would respectively take up a circular sector(half section). This implies doubling the number of tubes and in casealso of the cooling or heating fluid feed and drawing off ducts 14 and16, respectively, as well as of the connecting pipes 19.

This tubes arrangement may be well suited for extremely exothermic orendothermic reactions as it allows to have two feeds and extractions forthe cooling or heating fluid, thus increasing the heat exchangeefficiency.

In this respect, arrangements with three or more coil-shaped tubes 13arranged side-by-side in correspondence of a same horizontal plane mayalso be advantageously foreseen.

In FIG. 8, a further embodiment is shown of the side-by-side tubearrangement.

In this case, the two tubes 13 arranged side-by-side along apredetermined horizontal plane, comprise a first and a second tubeportion (13 a, 13 b) having the shape of an arc of circle of differentlength arranged near a central zone of the bed 3 and a peripheral zonethereof, respectively. Moreover, a plurality of third tube portions 13 cconnecting the second tube portion 13 b with the first tube portion 13 aare provided.

Preferably, the third tube portions 13 c are straight and extendradially from the second to the first tube portion.

According to this embodiment, only one feed duct 14 and one drawing offduct 16 are required. Both ducts 14 and 16 are disposed in the centralduct 10 and are in fluid communication with all the tubes 13 side byside.

Tubes 13 of the type shown in FIG. 8 allow very good heat exchangeefficiency. In fact, in addition to the advantages set forth withrespect to the tubes arrangement of FIG. 7, the cooling or heating fluidflows within tubes 13 in substantial pure co-current or counter-currentmotion with respect to the flow of reagents gases within the catalystbed 3, so as to improve the heat exchange efficiency.

Moreover, the presence of the radially extending plurality of tubeportions 13 c allows to advantageously reduce the pressure drop of thecooling or heating fluid flowing through tubes 13.

The reactor according to the present invention may be advantageouslyemployed for carrying out essentially all kinds of exothermic orendothermic reactions. In particular, examples of exothermic reactionsthat are well suited for being carried out with the present inventionmay be: methanol, ammonia, formaldehyde, organic oxidation (for exampleethylene oxide), whereas, examples of endothermic reactions may be:styrene and methylbenzene.

Fluids such as hot water, that transforms into steam at a high thermallevel, or melted salts or diathermal oils are preferably used fordrawing off the heat (in case of exothermic reactions). Analogous fluidsmay also be used for supplying heat in case of endothermic reactions.

The operation of the reactor 1 for carrying out exothermic orendothermic reactions according to the invention is describedhereinbelow.

It shall be noticed how the operating conditions of pressure andtemperature of the gaseous reactants fed to the catalytic bed 3 as wellas those of the cooling or heating fluid passing through the tubes 13are those conventional for the specific kind of reaction intended to becarried out, and therefore will not be described in specific detail inthe description below.

As an example, only the operating conditions for the methanol synthesisare given: synthesis pressure 50–100 bar, synthesis temperature 200–300°C., pressure of the steam generated 15–40 bar.

With reference to FIG. 1, a flow of gaseous reactants is fed to thecatalytic bed 3 through the gas inlet nozzle 9 and flows inside itthrough the perforated walls 4 and 7. The catalytic bed 3 is thencrossed with a mainly radial (axial-radial) motion by the gaseousreactants that react when they enter in contact with the catalyst.

The heat developed during the synthesis reaction or required forcarrying out such reaction is respectively drawn off or supplied by afluid passing through the tubes 13.

Such fluid is introduced into the reactor 1 through the nozzle 15 andfed to the lower tubes 13 of each group through the ducts 14. Then itpasses through the tubes 13 of each respective group that are connectedin correspondence of their free ends by connecting pipes 19, it is drawnoff from the upper tubes 13 of the respective groups through the ducts16 and evacuated from reactor through the gas outlet duct 11.

Finally, the flow of reacted gases obtained in the catalytic bed 3leaves the latter through the perforated wall 5, is collected in theduct 10 and then ejected from the reactor 1 through the gas outlet duct11.

The operation of the reactor 1 of FIG. 6 is analogous to that of FIG. 1,with the exception that the cooling fluid contemporaneously flowsthrough two series 20 and 21 of tubes 13 arranged side-by-side. Furtheron, as the tubes 13 of each series are all connected to each other, thecooling fluid is fed through a duct 14 in correspondence of a lower tube13 and goes up through all the catalytic bed 3 passing through the tubes13 before going out from the upper tube 13 in order to be drawn off fromthe reactor 1 through the nozzle 17.

Advantageously, it is important to notice that the tubes 13 extendwithin the catalytic bed 3 along a plane substantially parallel withrespect to the crossing direction of the catalytic bed by the flow ofgaseous reactants.

From the above description, the numerous advantages achieved by thepresent invention clearly arise, in particular the provision of areactor for carrying out exothermic or endothermic reactions which iseasy to realize, reliable and requires low investment and maintenancecosts, and at the same time allows to operate at a high conversionyield, low pressure drops, low energy consumption and with a highefficiency of heat exchange between the gaseous reactants and thecooling or heating fluid.

1. Isothermal reactor for carrying out heterogeneous exothermic orendothermic reactions, comprising: a preferably vertical, outer shell(2) of substantially cylindrical shape; at least one catalytic bed (3)provided in the shell (2) and comprising opposed perforated side walls(4, 5) for the inlet of a flow comprising reactants and the outlet of aflow comprising reacted substances, respectively; and at least one tube(13) passing through said at least one catalytic bed (3) for the passageof a cooling or heating fluid; characterized in that said at least onetube (13) extends within said at least one catalytic bed (3) along aplane substantially perpendicular with respect to the side walls (4, 5).2. Reactor according to claim 1, characterized in that said at least onetube (13) extends within said at least one catalytic bed (3) along asubstantially horizontal plane.
 3. Reactor according to claim 1,characterized in that said at least one tube (13) extends as aspiral-shaped coil.
 4. Reactor according to claim 3, characterized inthat said spiral-shaped coil has a winding pitch that varies inaccordance with the variation of the radius of the spiral.
 5. Reactoraccording to claim 4, characterized in that said winding pitch decreasesas the radius of the spiral increases.
 6. Reactor according to claim 1,characterized in that it comprises a plurality of tubes (13) arranged insaid at least one catalytic bed (3) at a variable distance betweenadjacent tubes (13).
 7. Reactor according to claim 1, characterized inthat it comprises a plurality of tubes (13) in said at least onecatalytic bed (3) overlaid with respect to each other and connected atrespective free ends.
 8. Reactor according to claim 6, characterized inthat said tubes (13) are connected to each other in groups of at leasttwo tubes, each group being in fluid communication with a duct (14, 16)for feeding and drawing off said cooling or heating fluid, respectively.9. Reactor according to claim 1, characterized in that it comprises aplurality of tubes (13) arranged side-by-side are provided incorrespondence of at least one predetermined plane substantiallyperpendicular with respect to said side walls (4, 5) within said atleast one catalytic bed (3).
 10. Reactor according to claim 9,characterized in that said at least two tubes (13) arranged side-by-sideextend as a coil having the shape of an arc of a circle of increasinglength from a central zone of said bed (3) to a peripheral zone thereof.11. Reactor according to claim 9, characterized in that said at leasttwo tubes (13) arranged side-by-side comprise a first and a second tubeportion (13 a, 13 b) having the shape of an arc of a circle of differentlength arranged near a central zone of said bed (3) and a peripheralzone thereof, respectively, and a plurality of third tube portions (13c) connecting said second with said first tube portion (13 b, 13 a).